Many decades ago, there used to be Vasai-walas carrying baskets full of fruits and vegetables from Vasai by train and selling them in Mumbai markets. They would start early morning harvesting fruits and vegetables from orchards. Vasai, near Mumbai was famous for growing fruits and vegetables. These freshly harvested produce would then be put in baskets and brought to Mumbai by train and sold in markets. These would have the best quality, including colour, flavour, nutrients and would provide the best eating experience.
During the past several decades, due to industrialisation and urbanisation of places like Vasai, the farms are gone, several hundred kilometres away from Mumbai. If the farmers tried to do the same thing that was done by Vasai-walas, the fruits and vegetables would become too soft due to over-ripening and would rot, making them unfit for consumption.
Fruits grow on the trees and as they become mature, they accumulate several substances including sugar, starch, other carbs including dietary fibre, protein, fats, vitamins and minerals as well as many other botanicals and pigments and fragrances etc. All these do not peak at the same time. Also, some of the substances formed earlier may be converted to something else so there will be decline in their concentrations.
At some point, they may have the maximum level of components that give us the best eating sensation. We call this ripe fruit. Unfortunately, fruit does not remain at this stage of ripeness too long. When we keep it longer, it becomes overripe and loses it eating quality and finally it becomes inedible.
When fruit is unripe and not yet mature, it is small, hard, green and sour e.g., mango also called kairee. It may be used for making pickle, panha (a sweet & sour drink) or dried mango powder (amchur) used along with spice for flavouring. It has the taste, texture and flavour very different from the ripe mango, which is soft, sweet, pleasantly flavourful and highly colourful from yellow to orange.
When unripe, fruit is hard because of carbohydrates that are insoluble in water. As most fruits begins to ripen, their starch starts hydrolysing to sugars. As sugars are soluble in water, there is softening experienced along with development of sweetness. Green colour is due to chlorophyll, which during ripening process starts degrading in most fruits and then the pigments underneath start to become visible. These are either carotenoids that are responsible to yellow, orange and red colours or anthocyanins that provide blue, purple, red etc. Ethylene is the ripening compound which is formed in fruits and it causes the changes such as breakdown of chlorophyll and softening of tissues by breakdown of carbs.
Many fragrance substances start building up providing typical fruit flavours. There are hundreds of different flavour compounds responsible for the overall fruit flavours. Even differences in the variety of fruit like banana, apple or orange would show differences in their flavours due to different composition of similar compounds.
Therefore, farmers would like their fruits in consumer market when they are at their peak of ripeness. The ripening process may be very short e.g., a few days or in some cases it may be a week or two or even longer. So, it is a difficult task to bring the fruits from hundreds of kilometres away. It takes several days after harvest till putting them on shelves in market. The farmers if they wait for ripening on tree, the fruits will become overripe and spoil before the consumers buy them. Therefore, they must harvest the fruits before ripening when they are hard.
When fruits are hard, they will withstand the damage during harvest, packing, transport and any other handling. After reaching the destination they may be allowed to ripen either naturally or by exposing them to ethylene which expedites ripening. However, it must be remembered that the optimum contents of nutrients, colour, flavour and other botanicals are developed in the fruits when they are ripened on the plant itself. Some changes can take place in fruits ripened after harvest such as softening and sweet taste in some fruits to make them acceptable for eating.
There are also other means of preventing spoilage or loss of quality during transport and storage before consumers buy the fruits and these are also employed to maintain the quality. Chilling is one such means. Modified or controlled atmosphere storage is another method.
Fruit like any other part of plant is a living thing and is continually respiring. It takes in oxygen from the air and gives off carbon dioxide. Even after harvest it continues respiration which helps provide energy needed for various changes taking place in the fruit. After harvest, if the fruits are kept in lower temperature, the respiration rate is slowed and changes taking place also are slowed down. Thus, fruits that are on tree at ambient temperature which may be environmental temperature of 30 or 40℃ or even higher, are respiring at very high rate and may continue this rate and would spoil soon. However, if after harvest, they are kept at lower temperature, say 10 or 20℃, their respiration rate is lowered and they last much longer without spoilage.
Similarly, if after harvest, they are kept in higher CO2 atmosphere, this also slows down their respiration rate and consequently the changes such as ripening and spoilage. So, farmers may try to delay changes by using any of these means while they are bringing them to market place. Once they are ready for marketing, waiting for them to ripen would cost both time and warehouse charges so fruits may be exposed to ethylene gas to ripen them faster. Use of calcium carbide that produces acetylene which also can ripen, is banned as it is unsafe and may cause health hazard.
In fruits, some fruits like banana, mango and apple, have plenty of starch when unripe. They are hard and resist damage. Upon ripening after harvest, this starch converts to sugar and so there is softening and sweet taste forming along with change of colour from green to yellow, orange or red. Citrus fruits however, lack starch, so they change the colour but sweet taste enhancement does not take place. So, these fruits need to form enough sugar on tree itself before harvest, otherwise upon ripening they will remain sour.
Thus, urbanisation has some of these problems of fresh fruits which to some extent are taken care by technology but the best fruits would be those that are ripened on plant itself, so one must visit the fruit orchards to enjoy the best fresh fruits.
Handbook of Postharvest Technology: Editors Chakraverty et al. 2003, Marcel Dekker
Adriana Gallego: How Fruit Ripens, 2023 (https://goldbio.com/articles/article/How-Fruit-Ripens)
Jeantet et al. Food Biochemistry & Technology, from Handbook of Food Science & Technology 3, 2016: John Wiley & Sons Inc.
Changes in Carbohydrate Content During Fruit Ripening: Chaimanee & Suntornwat, Biochemical Education 22(2) 1994, 101-102
Fruit Ripening from TNAU Agritech Portal: Horticulture (https://agritech.tnau.ac.in/horticulture/fruit_ripening.pdf)
Cruz-Hernandez & Paredes-Lopez, Fruit Quality: New Insights for Biotechnology, Critical Reviews in Food Science & Nutrition 52:272-289 (2012) (Fruit Quality: New Insights for Biotechnology: Critical Reviews in Food Science and Nutrition: Vol 52, No 3 (tandfonline.com))